In positioning control of a feed shaft of a machine tool and the like using a servomotor, according to a conventional method for preventing an overshoot during positioning, the output torque of a servomotor is reduced by decreasing a value of an integrator in a velocity loop when a position deviation becomes close to "0" (i.e., a movable part of the machine comes close to a commanded position), to thereby reduce the overshoot.
However, in a full-closed loop control, the position of the movable part driven by the feed shaft is detected by a position detector such as a scale detector for performing a positional feedback control based on the detected position. Further, in a case of such control a mechanical system between the servomotor and the position detector such as a scale detector may have an insufficient rigidity. If so, then the servomotor will, due to the torsion of the mechanical system, advance too much by an amount corresponding to the torsion at the time when the position deviation has become close to "0" and the movable part has reached the commanded position. That is, when the rigidity of the mechanical system between the servomotor and the position detector is insufficient, the movable part is driven while the mechanical system is distorted. The result is that, when the position is detected by the position detector as being the commanded position, the servomotor actually takes a position which makes the movable part to advance beyond the commanded target position by the amount corresponding to the torsion of the mechanical system. When the position deviation becomes "0" and the positioning is completed to stop the rotation of the servomotor, the torsion of the mechanical system is released gradually, causing the mechanical movable part to move further forward by the amount corresponding to the torsion of the mechanical system (in the same direction as it has been moving), thereby to overshoot the commanded target position. As the movable part of the machine moves forward, the position deviation increases. Therefore, in order to cancel the increase in the position deviation, the servomotor moves in the opposite direction, so that the movable part is positioned at the commanded target position. Thus, in the full-closed loop positional control, the movable part tends to overshoot the commanded position due to the torsion of the movable part.